(1) Field of the Invention
The present invention relates to a closure mechanism for a loose-leaf holder for sheets defining holes along an edge thereof, comprising a base plate carrying fixed, straight prongs for receiving the holes of the sheets and interconnected prongs pivotal between a closed position wherein they cooperate with the fixed prongs and an open position, and a spring engaging a connecting element of the pivotal prongs, the spring biasing the pivotal prongs into the closed position.
(2) Description of the Prior Art
In conventional closure mechanisms of this type, the spring biasing the pivotal prongs against their open position is held in the base plate and presses against the connecting element of the pivotal prongs, the connecting element usually being constituted by a bridge which is integral with the pivotal prongs and has a portion protrudingly offset from the plane of the bridge. The spring is held in a slot in the base plate, and this slot is arranged in a portion of the base plate facing away from the offset portion in relation to the pivoting axis of the bridge. The spring is further supported on a bead of the base plate arranged in the range of the geometric pivoting axis of the bridge. This arrangement produces relatively poor lever ratios, causing the spring to weaken relatively rapidly and to break.